Bar tacking is the term used to describe the sewing of small stitch patterns which are generally used for reinforcing joints in shoes and other garments. These patterns are generally limited to a specific number of stitches in the range of from 10 to 100 stitches per pattern and cover only a small area of the workpiece. The operation is performed by moving the workpiece under the needle and this motion is achieved automatically by means of a work clamp which is mounted for movement along two axes relative to the needle. Work clamp movement is controlled by a style or feed cam which is operatively linked to the clamp. The style cam is generally driven by means of a shaft connected to the main needle bar drive shaft through a gear train. Thread cutting is controlled by a second cam connected to the same shaft but mounted opposite to the style cam. In this manner a limited amount of automatic operation is achieved. However, the variety of patterns are limited by cam design and the gear ratio between the needle drive shaft and the cam shaft since each pattern must be completed within one rotation of the cam. This necessitates the replacement of the style cam for each change in pattern and in addition, if the number of stitches in the pattern changes, a new gear train must be installed. This may require anywhere from two to as long as eight hours effort by a skilled mechanic and results in a significant loss of production per machine.
The purpose of this invention, therefore, is to provide an automatic bar tacker which is free of the restrictions of the style cam, thereby eliminating the need for costly changes resulting in loss of production. This is achieved by the replacement of the style cam with a numerically controlled drive. The subject invention is intended to be easily installed on existing machines with as little modification of the sewing machine as possible